SEXUAL ACTIVITY OF MALE RABBITS 493 
TABLE 7 
Size of litters at different services 
Ist 5TH 10TH 157TH 20TH 
MALE NUMBER | Num- | Aver- | Num-| Aver- | Num-| Aver- | Num-| Aver- | Num- | Aver- 
ber age ber age ber age ber age ber age 
litters size litters size litters size litters size litters size 
1 6 6.66 6 6.00 1 (All 7 Hess], dul 4.27 
3 11 6.50 8 5) (43) 7 Uf fB0/ Pe 10.5 
4 8 Ye 6 6.16 6 nas) 4 5.9 6 5.00 
Aerial] GSteaes|ezo: 6.92 20 5.95 20 6.95 13 6.46} 17 4.53 
most noticeable and universal concomitants of heavy sexual serv- 
ice, but there is great divergency of opinion as to how frequent 
or how many copulations constitute ‘heavy service’ with vari- 
ous classes of domestic animals. Apparently in bringing about 
twenty services in three or four hours we have approacheda point 
which for the rabbit seriously curtails his ability to produce off- 
spring, and furthermore we have demonstrated in large part 
what is the direct basis for this curtailment. 
SIZE OF LITTER 
Having observed the described changes in the vital properties 
of the sperm in semen from advanced services, and also what is 
probably in large part a result of the same, namely, the reduced 
likelihood of pregnancy resulting from the more advanced serv- 
ices, 1t would seem a priori to follow that the number of young 
per litter would likewise undergo a reduction as the number of 
copulations increases. Table 7 presents the facts in regard to 
this matter. 
Inspecting the columns up and down reveals no superiority of 
one male over another. Inspecting the horizontal rows reveals 
no marked effect of number of copulations on litter size; in fact, 
it may be questioned if it reveals any significant reduction. 
Certainly any falling off in litter size up to the 15th service is 
impossible to detect by inspection, but a very perceptible drop 
occurs between the 15th and 20th service. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 25, No. 2 
